diff --git a/tmux.h b/tmux.h
index c60a044..ae356aa 100644
--- a/tmux.h
+++ b/tmux.h
@@ -25,6 +25,7 @@
 
 #include <sys/time.h>
 #include <sys/uio.h>
+#include <sys/types.h>
 
 #include <event.h>
 #include <limits.h>